1. Field of the Invention
This invention relates to a fluid-impermeable composite hose. More particularly, it relates to a fluid-impermeable composite hose having a fluid-impermeable laminated layer formed of a laminated sheet containing a metallic foil, or a metallic layer formed by vapor deposition. The hose of this invention is particularly useful as a fluid-impermeable hose for transporting any of various kinds of fluids in a motor vehicle.
2. Description of the Related Art
Every hose used for transporting a refrigerant in an air-conditioning system on a motor vehicle is required to be impermeable to the refrigerant. This is particularly the case with any hose for transporting e.g. an alternative to chlorofluorocarbons, or carbon dioxide as a refrigerant in view of system maintenance, environmental protection, etc. One of the most effective approaches is a hose having a laminated wall layer containing a metallic foil, or a metallic layer formed by vapor deposition. Environmental protection also requires a fuel hose to be impermeable to fuel, and a laminated wall layer is very useful for a fuel hose, too.
It has been usual to form a laminated wall layer for a hose by longitudinal lapping or spiral winding of a tape of a laminated sheet containing a metallic foil, or a metallic layer formed by vapor deposition. Longitudinal lapping is a method in which a tape of a laminated sheet having a width large enough to encircle a hose to be made is placed in parallel to the longitudinal axis of the hose and bent into a cylindrical layer having a pair of overlapping edge portions. Spiral winding is a method in which a tape of a laminated sheet is wound in a spirally overlapping way to form a cylindrical layer.
Longitudinal lapping has a number of advantages over spiral winding, as stated below. First, a cylindrical layer can be formed more rapidly by longitudinal lapping. Then, it can be carried out in tandem with a step of rubber extrusion preceding or following it. Moreover, the overlapping edge portions formed by longitudinal lapping have a smaller length which means that a hose has a higher fluid impermeability.
A laminated sheet is, however, a multilayer structure having spring elasticity. While it does not exhibit a very high bending resistance for spiral winding, it exhibits a high bending resistance for longitudinal lapping as it has to be bent across its width. Its bending resistance tends to cause the separation of the overlapping edge portions from each other. As a result, it is likely that a hose having a layer formed by longitudinal lapping may not retain an accurately circular shape in cross section, but may have a deformed circular shape. Moreover, the separation of the overlapping edge portions joined together may result in the failure of the hose to retain its fluid impermeability. Even if an intermediate rubber layer, or a thin resin layer may be extruded about the laminated layer, its binding force is not sufficiently strong to overcome the bending resistance of the laminated sheet.
Moreover, a hose having a laminated layer formed by longitudinal lapping is less easy to bend, since the overlapping edge portions of the laminated sheet extend longitudinally of the hose. In other words, it is usually inferior in overall flexibility to any hose having a spirally wound wall layer.
It is, therefore, an object of this invention to overcome those drawbacks of any fluid-impermeable composite hose having a fluid-impermeable laminated layer formed by longitudinal lapping of a tape of a laminated sheet which are due to the high bending resistance of the overlapping edge portions of the laminated sheet, as pointed out above. It is another object of this invention to improve the overall flexibility of any such fluid-impermeable composite hose.
The inventors of this invention have found that it is effective to bind a longitudinally lapped tape of a laminated sheet by winding thread about it at a low density. The inventors have also found that it is effective to line a laminated layer with a rubber layer and rely upon its elastic deformation for causing the strong binding force of the wound thread to make constrictions in the laminated layer.
According to a first aspect of this invention, there is provided a fluid-impermeable composite hose having a wall comprising a laminated layer formed of a laminated sheet which contains a metallic foil, or a metallic layer formed by vapor deposition, wherein the laminated layer is formed by longitudinally lapping a tape of the laminated sheet, and is bound with thread wound about it at a density not exceeding 20%. The high bending resistance of the laminated sheet is effectively suppressed by the thread wound about it. Therefore, there is no deformation of the hose in its cross sectional shape. Moreover, there is no separation of the overlapping edge portions of the laminated layer which may cause the loss of the fluid impermeability of the hose.
The thread is essentially different in construction and effect from any reinforcing yarn layer formed usually on a hose. The reinforcing yarn layer is intended for improving the strength of the hose. It is formed of reinforcing yarn wound spirally or braided at a high density, even though it may lower the flexibility of the hose to some extent or other. On the other hand, the thread employed according to this invention is wound only at a density not exceeding 20%, and does not lower the flexibility of the hose. It is exclusively intended for suppressing the bending resistance of the laminated layer, and its density not exceeding 20% is sufficient for that purpose.
According to a second aspect of this invention, there is provided a rubber layer on an inner periphery of the laminated layer, and the laminated layer has constrictions formed by the thread owing to the elastic deformation of the rubber layer. The constrictions make the hose easier to bend and improve its flexibility. If the thread is wound at a high density, the constrictions do not have a sufficiently large depth to improve the flexibility of the hose effectively. The thread density not exceeding 20% is, however, low enough to ensure that the constrictions have a sufficiently large depth to improve the flexibility of the hose effectively. The constrictions are very unlikely to cause e.g. the fracture of the metallic foil in the laminated layer unless the hose is repeatedly subjected to an extremely high pressure or large displacement. Thus, the hose is particularly suitable for use as, for example, a fuel hose which is unlikely to be subjected to a high pressure or a large displacement.
According to a third aspect of this invention, the constrictions are formed by the tension of the thread and/or its dry heat contraction. These are particularly effective ways of forming the constrictions. The constrictions formed by the tension of the thread are formed when it is wound, while those formed by its dry heat contraction are formed when the hose is heated as for curing.
According to a fourth aspect of this invention, the laminated layer has a smooth outer surface not having any constriction formed by the thread. Such a laminated layer is particularly unlikely to have its metallic foil broken when the hose is repeatedly subjected to a high pressure or a large displacement, though it cannot be expected to give the hose any such improved flexibility as is given by the constrictions in the second aspect of this invention. Thus, the hose is particularly suitable for use as a refrigerant hose which is very likely to be repeatedly subjected to a high pressure, or a large displacement, especially a hose for a carbon dioxide refrigerant. The laminated layer is preferably lined with a layer of a resin, or any other hard material which is not easily deformable, while the thread is preferably of a material having only a low degree of dry heat contraction, so that the laminated layer may retain a smooth outer surface, while the thread can bind the laminated layer strongly enough to overcome the bending resistance of its overlapping edge portions joined together.
According to a fifth aspect of this invention, the thread is preferably of polyethylene terephthalate (PET), polyamide (PA), rayon, aramid (aromatic polyamide), polyethylene naphthalate (PEN), or polyvinyl alcohol fibers.
The thread for binding the laminated layer may be of any kind, however, it is desireable to use the thread of PET, PA, rayon, aramid, PEN, or polyvihyl alcohol fibers as in the fifth aspect.
According to a sixth aspect of this invention, the laminated sheet is preferably composed of a resin film laminated on (1) a metallic foil, (2) a metallic foil and a reinforcing material, or (3) a metallic layer formed by vapor deposition. The combination of a metallic foil and a reinforcing material is particularly preferred for the laminated layer having constrictions formed therein.
The above and other features and advantages of this invention will become more apparent from the following description and the accompanying drawings.